Medical procedures involving access to the brain through a burr hole in the skull are used to treat a variety of medical conditions. For example, burr holes may be formed to allow implantation of a catheter, e.g., an intraparenchymal (IPA) catheter, to deliver a therapeutic agent (infusate) to a target tissue region within a mammalian brain for the treatment of neurological ailments.
Use of an IPA catheter to deliver a therapeutic agent to the brain generally involves the insertion of the catheter into the brain and dispensing the agent at the desired target region. During a typical implantation procedure, an incision may be made in the scalp to expose the patient's skull. After forming a burr hole through the skull, the catheter may be inserted into the brain. To accurately place the catheter and avoid unintended injury to the brain, surgeons typically use stereotactic apparatus/procedures. One exemplary stereotactic apparatus is described in U.S. Pat. No. 4,350,159 to Gouda, which may be used to position, for example, an electrode. A cannula or needle may be located and held with the stereotactic equipment, after which the catheter may be inserted through the cannula. Once a distal tip of the IPA catheter is correctly located, the cannula may be removed, leaving the catheter in place.
While effective for delivering substances to the desired location in the body, care must be taken during implantation and therapy delivery to ensure that backflow of the therapeutic agent is minimized. “Backflow,” as used herein, refers to portions of the therapeutic agent delivered by the delivery tube (e.g., catheter) that tends to flow back along the outer diameter of the body of the delivery tube (e.g., towards its proximal end) instead of infusing into the intended target tissue region surrounding the distal tip of the catheter.
While the degree of backflow may vary, it may become severe if the infusate finds a path into the Cerebral Spinal Fluid (CSF). If such a path is formed, the infusion pressure may drop dramatically (e.g., until it equals CSF pressure).
In addition to reducing the efficacy of the treatment (e.g., less than the desired volume of therapeutic agent is delivered to the intended target tissue region), backflow may further result in substance delivery to unintended regions of the body, e.g., other regions along the catheter length. Moreover, the volume of substance that backflows is basically wasted, a consequence which is particularly undesirable when the therapeutic agent is expensive or otherwise difficult to obtain.
Many conventional catheters are furthermore designed for treatment of acute conditions. As a result, they are often configured for temporary implantation and are frequently constructed of generally rigid materials that are not amenable to modification (e.g., trimming) during the actual implant procedure as may be required for longer term implantation. The ability to modify the catheter length would be advantageous for implantation of catheters associated with long term (chronic) therapy.